1. Field of the Invention
This invention relates to sensing the position of an object placed within a living body. More particularly, this invention relates to detection and compensation for artifacts experienced during position sensing of a probe in a living body.
2. Description of the Related Art
A wide range of medical procedures involve placing objects, such as sensors, tubes, catheters, dispensing devices, and implants, within the body. Realtime imaging methods are often used to assist doctors in visualizing the object and its surroundings during these procedures. In most situations, however, realtime three-dimensional imaging is not possible or desirable. Instead, systems for obtaining realtime spatial coordinates of the internal object are often utilized.
Many such position sensing systems have been developed or envisioned in the prior art. Some systems involve attaching sensors to the internal object in the form of transducers or antennas, which can sense magnetic, electric, or ultrasonic fields generated outside of the body. For example, U.S. Pat. No. 5,983,126 to Wittkampf, whose disclosure is incorporated herein by reference, describes a system in which three substantially orthogonal alternating signals are applied through the subject. A catheter is equipped with at least one measuring electrode, and a voltage is sensed between the catheter tip and a reference electrode. The voltage signal has components corresponding to the three orthogonal applied current signals, from which calculations are made for determination of the three-dimensional location of the catheter tip within the body. Similar methods for sensing voltage differentials between electrodes are proposed by U.S. Pat. No. 5,899,860 to Pfeiffer, whose disclosure is incorporated herein by reference. In both of these systems, it is necessary to undertake a separate calibration procedure in order to adjust for discrepancies between the apparent position of the catheter tip as measured and its actual position.